1. Field of the Invention
This invention relates to a composition for use in the production of acetylene gas and a method for treating the lime slurry by-product from acetylene gas production to make the slurry easier to handle and avoid the need for special handling equipment for the sediment. The present invention allows an acetylene producer to use calcium carbide from a variety of sources and allows the calcium carbide producer more flexibility in sourcing raw materials.
2. Art Related to the Invention
Calcium carbide (CaC2) is produced in an electric furnace by heating a mixture of lime and carbonaceous materials such as coke, coal, or charcoal. The heat of the furnace converts the mixture to calcium carbide and carbon monoxide. Both the source of lime and the source of carbonaceous material have different impurities which are carried through to the calcium carbide. Typically, industrial grade calcium carbide, sold for the generation of acetylene gas, contains about 2% to about 5% by weight impurities. The primary impurities are metals and metal alloys such as silicon, iron, aluminum and magnesium.
One of the conventional methods for producing acetylene (CHxe2x89xa1CH) is the action of water on calcium carbide. One of the by-products from such production is a lime slurry. This lime slurry essentially comprises calcium hydroxide, water, and whatever impurities were present in the calcium carbide.
The lime slurry is pumped from the reactor to settling tanks where water is removed for recycling and sediment forms. Water from the slurry is saturated with acetylene and is therefore preferred as a source of water in the reactor. By using recycled water, the overall efficiency of the reaction is increased. Thus, it is important that the slurry settle rapidly and form the sediment.
Once water has been removed from the slurry for recycling and the sediment formed in the holding tanks, water is added to the sediment to reslurry the sediment and make the sediment easier to pump.
It has been found that the lime slurry and the resulting sediment have different physical characteristics, especially settling characteristics and reslurrying characteristics, depending on the source of calcium carbide. These different characteristics have been attributed to the impurities which are present in the calcium carbide. For example, when the calcium carbide is produced from petroleum coke, the lime slurry settles slowly, the sediment is diffuse and readily reslurries. On the other hand, when metallurgical coke is used to make the calcium carbide, the lime slurry settles quickly, the sediment is dense and is difficult to reslurry.
Because of the differences in the settling properties of the lime slurry and the reslurrying characteristics of the sediment, different mechanical equipment is employed to handle the sediment. Thus, acetylene producers generally do not switch calcium carbide sources. Furthermore, calcium carbide producers are forced to standardize their sources of raw materials so as to maintain the same type of impurities in their calcium carbide. Needless to say, this means that the calcium carbide manufacturers are unable to switch their sources of raw material, thereby increasing the overall cost for production of calcium carbide which, in turn, increases the overall cost for production of acetylene.
There is a need for a simple and inexpensive way to treat the lime slurry by-product from the acetylene manufacturing process so as to increase the settling rate while improving the handling properties of the sediment which results from the lime slurry so as to reslurry readily and to be easy to handle, even after sitting a number of days in the holding tanks.
It has now been discovered that a settling aid, present in the reactor during production of acetylene, can effect the settling property of the by-product lime slurry and can effect the handling properties of the sediment. The use of the settling aid of the present invention has been found to increase in the rate of settling of the lime slurry, thus increasing the rate of recycling of water from the slurry. It has also been found to improve the reslurrying properties of the sediment thereby assisting in removal and handling of the sediment.
Specifically, it has been found that by employing the present invention, no special equipment is necessary for handling the lime slurry or the sediment that results from the lime slurry. Furthermore, it has been found that the acetylene manufacturer may vary the sources of calcium carbide without having to modify or change the lime slurry and sediment handling equipment. The present invention also allows the calcium carbide manufacturer to vary the sources of raw material. Both of these allow for lower production costs of calcium carbide and acetylene.
Furthermore, it has been found that by employing the present invention there is no detrimental effect to the reactor or the reaction that occurs in the acetylene reactor. The settling aid, although present in the reactor, does not affect the rate of reaction and has been found to carry through the reactor and into the lime slurry.
Furthermore, it has been found that the settling aid settles with the sediment and is not carried through into the recycled water. All this allows the acetylene manufacturer to continue his operations as normal with the improved benefit of allowing him to change the sources of calcium carbide.
Additionally, it is important that the sediment can be reslurried after a period of time. It has been found that the sediment of the present invention can sit for a number of days and still be reslurried and effectively pumped.
The settling aid of the present invention can be added directly to the acetylene reactor by the acetylene manufacturer or it can be added to either or both of the reactants, calcium carbide and water, prior to introduction into the acetylene reactor.
The settling aid may also be added directly to the lime slurry as it leaves the reactor, however, it is preferred that the settling aid be present in the reactor during the formation of the lime slurry.
It has also been discovered that the settling aid can be added to the top of the sediment in the holding tank prior to reslurrying the sediment and that such top treatment will beneficially effect the reslurrying properties of the sediment. Since such a treatment only effects the handling properties of the sediment and not the initial settling properties of the lime slurry and recycling of water to the reactor, it is not a preferred embodiment of the present invention.
The calcium carbide manufacturer can form a mixture of the calcium carbide and the settling aid and sell the mixture to the acetylene manufacturer. This allows the calcium carbide manufacturer to vary the source of raw material used to make calcium carbide without troubling the acetylene manufacturer.
Suitable settling aids for use in the present invention comprise phosphates, chelating agents, alkali metal chlorides, carbonates, carboxylic acids, sulfur compounds, clays, sugars, silica fume, and lignin.
Broadly, the present invention is a method for treating a lime slurry by-product from acetylene production to make the lime slurry and its resulting sediment easier to handle, said method comprising:
reacting water with calcium carbide in a reactor to form acetylene and a lime slurry by-product in the presence of a settling aid; and
recovering said lime slurry by-product with said settling aid present therein.
The method of the present invention can also be broadly defined as an improvement in the method for making acetylene gas from calcium carbide and water where a lime slurry is a by-product, the improvement comprising:
reacting said water and said calcium carbide in a reactor in the presence of a settling aid to form acetylene gas and a lime slurry by-product; and
recovering said lime slurry by-product with said settling aid present therein.
The method of the present invention can also be characterized as treating a lime slurry by-product from an acetylene manufacturing process or a sediment from the lime slurry by-product from the acetylene manufacturing process with a settling aid to improve the settling properties of the lime slurry and the handling properties of the sediment.
Thus, the present invention can be characterized as a new use of a settling aid where that new use is as an additive to an acetylene reaction and/or the by-product lime slurry and sediment.
The present invention has also led to discovery of a new composition for use in the production of acetylene, that composition being broadly defined as comprising a homogeneous mixture of calcium carbide and a settling aid.
As brought out above, it has been found that the settling aid which is present in the reactor ends up in the lime slurry, is carried into the settling tanks and ultimately stays with the sediment in the settling tanks. Thus, it is not carried away with the recycling water. Furthermore, it has been found that a number of the settling aids are environmentally friendly and, thus, the sediment with the settling aid therein is readily disposable without the need for further handling or treatment of the sediment.
Furthermore, it has been found that the present invention has no detrimental effect on the recycle water and, in fact, has the beneficial effect of increasing the rate of settling thereby increasing the rate of availability of the recycle water.
These and other aspects of the present invention may be more fully understood by reference to the following drawings and detailed description of the invention that follows.